Separation of hydrocarbons



Oct. 19, 1943. T. A. PETRY lawn.v 2,332,493

' SEPARATION oF"HYDRoqARBoNs Filed Feb. 5, 1941 ORNEY Patented cto is. i943 para SEERATHON 0F ROCARBQNS Application February 5, 1941, Serial No. @7AM d Claims. (Cl. mi2-d2) This invention has to do with the separation of K aromatic and non-aromatic hydrocarbons of substantially similar boiling points by methods of azeotropic distillation, wherein the distillation is conducted in the presence of an added material,

herein referred to as an azeotropic agent, which,

forms constant boiling mixtures with the 'nonaromatic hydrocarbons which constant boiling mixtures boil below -th boiling point of the aro matic hydrocarbon or of any constant boiling mixture which may be formed therewith.

In such distillations, the aromatic material is This invention has for its object the provision of a methodffor conducting such azeotropic distillations wherein a lessened use .of reflux is permitted with the attainment of a given purity of section 2 and an exhausting section 3. A feed material is brought to the system by pump 4 and an additive or azeotropic material by pump 5t A portion of the azeotropic material passes through pipe t to join the feed in pipe 1, the resulting mixture being heated to distillation temperature in heater 8 and introduced to the column` at feed level E. The vapors rising from 9 through the rectification section 2 under the in-V uence ,of wet reux intr uced at I il are freed of still bottom product and are withdrawn by pipe H and pass through condenser I2 to receiver .i3 whence overhead product is withdrawn at lll and reflux is returned to the column by pump vI-5. Still bottomsv product descending through the exhausting section 3 is freed of overhead product by the joint action of the heat introduced through reboiler AIli and of azeotropic agent in vapor form derived from pipe ill," vaporstill bottom product and in which the azeotropic agent addition is under relatively precise control.

It has for a major object the use of at least a portion of the azeotropic agent by introducing it to the system in vapor form.

The usual form of process for conducting such azeotropic processes has heretofore been thatof introducing a heated feed mixture, consisting of the desired aromatic material, the undesired nonaromatic material, and a predetermined amountA -of azeotropic agent at some point between the ends of a continuously operating fractionating head product, and heat is applied to the exhausting column by means of a. reboiler.

V This invention is based upon a modication of 'izedin heater I8 and` introduced as vapor at i9.

still bottom product is withdrawn by pipe 26.

This form of operation has the decided advantage over the previous operation in that the presence of azeotropic agent in vapor form in the` exhausting column enables a greater degree of separation of still overhead product from still bottom product with the same overall amount of azeotropic material being used in the system without increase in reflux ratio. `A further very ysignificant advantage rises from the very precise control over the `amount of azeotropic agent which is introduced to the system. Since the overall eiliciency of the system/ depends upon rather precise control of this amount, it may be quite conveniently achieved here by a constant setting of volume passed at control point 2l in this system in which a portion of the azeotrcpic l agent is introduced in vapor form intothe exhausting column to act as a stripping medium therein. Y j

The invention may be understood by reference to the attached drawing, the single gure of which shows the process in diagrammatic form. In this drawing i is a fractionating column adapted for continuous operation consisting of a rectification pipe 6 and a variable control responsive to variations in the system, either manual or automatic, at controlpoint 22 acting upon a lesser amount of azeotropic agent, say on about 10% of .the total.

Referring specifically to the separation of toluene from e. close cut fraction of petroleum origin, in the presence' of methanol, to which this system of operation is Nquite adapted, and assuming a feed of about 45% concentration of toluene, for volumes of feed, about 60-80 volumes of methanol, total, would be utilized, of which about 6-8 volumes or less would be passed into the bottom of the column as vapor. In a column -of about 24 theoretical plate eiciency, the opera- In this specification and the claims, the term "constant boiling mixture" is made use of in full recognition of the fact that the non-aromatic hydrocarbons so removed are themselves a mixture and when considered from the standpoint of precision the term "constant boiling is inexact. However, for any comercial distillation, and particularly for a continuously operating commercial distillationfthe variations are sumciently small that the material may be readily handled from the design and operating standpoint as a constant boiling mixture, and the term is used with that understanding.

Since with hydrocarbon fractions having low aromatic contents it is frequently desirable to conduct the azeotropic distillation in two steps, recovering as a still bottom from the first step a fraction more concentrated in aromatic and as a still bottom from the second step the desired aromatic in a condition of relatively high purity, the distillation conditions in the two steps being similar except for the necessary variations in azeotropic agent amount, etc., dependent upon the different concentrations of aromatic in the feed the invention is to be understood as being applicable equally to such two-step azeotropic distillation operations.

We claim: v

l. That method of conducting a distillation separation of an aromatic hydrocarbon material from non-aromatic hydrocarbons of substantially similar boiling point in the presence of an added material which forms constant boiling mixtures with the non-aromatic hydrocarbons which constant boiling mixtures boil below the aromatic hydrocarbon or any constant boiling mixture formed therewith which comprises heating a feed stock comprising the aromatic and non-aromatic hydrocarbons to distillation temperature, introducing said feed to a continuously operating fractionating column between the ends thereof, adding a ,portion of the said added material to the -feed prior to heating, and adding the remainder of the saidadded material in vapor form near the bottomof the exhausting section of said fractionating column.

2. That method of conducting a distillation separation of an aromatic hydrocarbon material from non-aromatic hydrocarbons of substantially similar boiling point in the presence of an added material which forms constant boiling mixtures with the non-aromatic hydrocarbons which constant boiling 4mixtures boil below the aromatic hydrocarbon or any constant boiling mixture formed therewith which comprises heating a feed 5 stock comprising the aromatic and non-aromatic hydrocarbons to distillation temperature, introducing said feed to a continuously operating fractionating column between the ends thereof, adding a major portion of the added material to the feed prior to heating, and adding the remainder of the said added material in vapor form near the bottom of the exhausting section of said fractionating column. Y

3. That method of separating substantially pure i5 toluene from a close cut petroleum fraction containing the same which comprises heating the petroleum fraction to distillation temperature and introducing it to a continuously working fractionating column between the rectiiwing and exhausting sections thereof, and supplying methanol to the distillation system in sufficient quantity to effect a separation of non-aromatica from toluene, in which a major portion of the methanol is introduced into the petroleum fraction prior to heating thereof, and a minor portion of the methanol is introduced in vapor form near the bottom of the exhausting section of said column. 4. That method of conducting a. distillation separation of an aromatic hydrocarbon material from non-aromatic hydrocarbons of substantially similar boiling point in the presence of an added material having the azeotropic distillation characteristics of methanol under the conditions of operation appropriate for toluol recovery, which forms constant boiling mixtures with the nonaromatic hydrocarbons which constant boiling mixtures boil below the aromatic hydrocarbon or any constant boiling mixture formed therewith, which comprises heating a feed stock comprising the aromaticrand non-aromatic hydrocarbons to distillationv temperature, introducing said feed to a continuously operating fractionating column between the ends thereof, adding a portion of the said added material to the feed prior to heating, and adding the remainder of the said added material in vapor form near the bottom of the exhausting section of said fractionating column.

THEODOR A. PETRY. HENRY D. NOLL. RUSSELL LEE. 

